Quote:
Originally Posted by aerohead
brucepick,it does function exactly like the raised tailgate.
If the trailing edge is close to the template the spoiler captures the low-pressure vortex and isolates that low pressure in front of it,preventing it from communicating that pressure to the wake behind which would otherwise lower the base pressure,increasing the delta-P across the car,increasing drag.
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When the outer flow does separate at the trailing edge of the spoiler, it has decelerated to a lower velocity/higher pressure ( that evil Daniel Bournoulli ) leaving the base pressure of the wake higher,the delta-P lower,an concomitant lower drag.
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This raises questions for me. The tuft testing I have done of my sixth gen Civic coupe shows a recirculation zone for about 4 or 5% of the lid/window area near the spine of the car. Air reattaches a few inches before detaching from the trailing edge of the trunk lid. Good. And better than I thought. Certainly a solid well-placed surface is better than a recirculation zone for allowing air to slip along, no? Certainly the longer, descending-angled raised lid and lip would slow the air more than the 4" where the air currently reattaches, therefore gaining the pressure benefits you describe here, no? It seems to me the key is making sure the contours of a raised lid do not add drag, and if they don't that a 2% drag reduction should be possible. Modest, but measurable in FE terms in a careful test, no?